1. Field of the Invention
This invention relates to tree trimming apparatus which is especially suitable for trimming rights-of-way adjacent to electric power lines at a selected distance from the ground. In a preferred embodiment, the apparatus is airborne and includes an articulated boom for suspension beneath a helicopter undercarriage, with ten or more rotating circular saw blades mounted in coplanar, closely spaced, tandem relationship on the boom. The circular saw blades are powered by an internal combustion engine mounted on a drive, or engine section assembly of the boom and are linked to the engine by specially designed Gates "polychain" belts. The circular saw blades extend about ten inches out from the boom structure and thus permit the cutting of large tree branches which are six to eight inches or more in diameter, as well as smaller woody growth.
The boom-mounted circular saw blades rotate in a vertical plane when operational, with all blades oriented outwardly of the supporting boom. The blades each rotate on a separate shaft which is cantilever-mounted in the boom, such that the outside surfaces of the blades are located in a common plane. Accordingly, as the helicopter passes along the edge of a row of trees to be cut, the circular saw blades are always oriented on the tree side of the boom and are adapted to engage and cut the branches through. The severed branches then fall away on the boom side of the tree trimming apparatus. The articulated boom may be constructed of multiple sections, each section carrying one or more rotatable, belt-driven circular saw blades and the saw-carrying boom sections may be reversed top to bottom on the ground, in order to move the blades to the desired cutting side of the helicopter. However, in a preferred embodiment of the invention, ten circular saw blades are rotatably mounted on the bottom 20 feet of a single 30 foot boom, while the top 6 feet of the boom receives the engine assembly. In the absence of a significant tail-wind, the usual operational practice is to fly the helicopter along one side of a power line, trimming the tree branches and woody growth at a selected height for several miles and return in the opposite direction to cut the branches and woody growth on the opposite side, without shifting the circular saw blades from right to left.
When using a tree trimming apparatus having ten circular saw blades, each having a diameter of about two feet, the engine used to drive the blades should be capable of operating the blades at approximately 2300 to 2500 rpm. The inertia of the circular saw blades is a very significant factor in the cutting efficiency thereof, and due to the relatively great total weight and large blade diameter of these tandem-mounted blades, this factor aids in cutting tree branches of both small and large diameter.
It should be noted that the pivotal mounting of the articulated boom in the airborne tree trimming apparatus about a transverse axis which is substantially perpendicular to the direction of motion of the helicopter, not only aids in take-off and landing of the apparatus, but also permits the apparatus to yield slightly to the rear when encountering numerous or large branches during airborne operation. Thus, while the helicopter speed may be five to ten feet per second, the forward cutting speed of the circular saw blades through very large branches along a flight path beneath the helicopter may be somewhat less than this speed. The greater the average speed which is attainable for the helicopter at effective cutting rates, the more cost-effective the clearing operation will be.
The problem of encroachment of trees and other woody growth in power line rights-of-way and other locations which need to be kept free of trees and brush has been commonly solved with ground or air-applied herbicides. Helicopters have long played a large and important role in spraying herbicides to prevent the encroachment of trees and plants on such rights-of-way. However, the spraying of herbicides for woody growth control is sometimes undesirable, particularly during windy weather, since the herbicide is sometimes blown from the rights-of-way onto adjacent crops and animals. The alternative of cutting encroaching tree branches and other woody growth by use of ground vehicles or on foot has proved to be very expensive and time-consuming, particularly in remote areas.
2. Description of the Prior Art
The use of multiple, airborne, hydraulically-operated circular saw blades mounted on a boom for use in trimming trees along power line rights-of-way is detailed in U.S. Pat. No. 4,554,781, dated Nov. 26, 1985, to Randall Rogers. A ground-operated apparatus for trimming trees in orchards and in like applications is detailed in U.S. Pat. No. 4,067,178, dated Jan. 10, 1978, to Charles Miller. While perhaps suitable for use in the orderly environment of a fruit orchard, such ground vehicle-mounted apparatus is of limited use in trimming trees adjacent to electric utility rights-of-way in rural and remote areas. Furthermore, the apparatus such as that detailed in U.S. Pat. No. 4,067,178 is clearly not adaptable for mounting on a helicopter or other aircraft. A number of other patents disclose multiple circular saw blades for tree trimming purposes, the most pertinent of which patents are listed below. These patents detail non-coplanar, circular saw blades which are used in controlled, ground vehicle-supported tree trimming operations:
______________________________________ U.S. Pat. No. Patentee Date Issued ______________________________________ 3,487,615 C. O. Leydig, et al April 1, 1968 3,913,304 Paul Jodoin October 21, 1975 3,952,485 L. R. McRobert April 27, 1976 4,302,922 H. F. Guerndt Jr., et al December 1, 1981 ______________________________________
The present invention permits rapid and accurate trimming of trees adjacent to electric utility and other rights-of-way in a safe and efficient manner. The trimming height of the tandem array of airborne, engine-driven, coplanar circular saw blades may be forty feet or more, with the use of twenty blades in each array. The circular saw blades are designed to complement each other and to cause one blade to continue a cutting which is begun by an adjacent blade, where necessary in cutting large limbs. In use, an articulated boom carrying the tandem-mounted circular saw blades and attached to a helicopter will slope slightly rearwardly from the attachment point at the helicopter and from the articulated joint along a flight path beneath the helicopter, so that very small branches and woody growth cannot pass between any two adjacent blades without being cut. A primary factor in the cutting efficiency of these circular saw blades is the combined great weight and large size of the blades, which aggregation of mass creates a momentum or impetus which equals the product of the mass and the rotational velocity of the blades and greatly enhances the blade cutting efficiency. Take-off and landing with the apparatus is a simple matter for a qualified helicopter pilot due to the front-to-rear articulation of the operating boom with respect to the boom extension, permitting the apparatus to be laid out on a pair of ground-supported cradle supports beneath the helicopter at take-off or landing.
In addition to providing the above described features and advantages, it is an object of this invention to provide a self-contained tree trimming apparatus for suspension from, and towing by a helicopter and characterized by a downward-hanging boom carrying a plurality of adjacent, internal combustion engine-powered circular saw blades arranged in tandem to provide a cutting path or swath in woody growth, of from about twenty to about fifty feet in height along a predetermined flight path.
It is another object of the invention to provide a helicopter-mounted tree trimming apparatus fitted with multiple, internal combustion engine-driven circular saw blades mounted in tandem, substantially coplanar relationship on a substantially vertical, articulated boom. The boom is mounted on the helicopter to prevent substantial rotation about its longitudinal axis and is articulated to permit pivoting in a vertical plane beneath the helicopter, which vertical plane substantially bisects the flight path of the helicopter.
Yet another object of this invention is to provide an airborne tree trimming apparatus which is fitted with a governor controlled internal combustion engine and multiple circular saw blades located on one end of an articulated operating boom, the blades being connected by a system of belts to the engine, wherein a quick release hook attached to the helicopter supports the top end of the boom and a safety cable extending through the boom and permits the apparatus to be jettisoned from the helicopter in an emergency.
Still another object of the invention is to provide a self-contained, helicopter-mounted tree trimming apparatus which is capable of operating independently of the helicopter and is provided with multiple circular saw blades arranged in tandem on a substantially vertical operating boom and powered by a governor-controlled internal combustion engine also mounted on the operating boom above the circular saw blades, the circular saw blades being sufficiently large and heavy to generate significant momentum and inertia for optimum cutting efficiency.